A chapter is one of the main divisions of a piece of writing of relative length, such as a book of prose, poetry, or law. In each case, chapters can be numbered or titled or both. An example of a chapter that has become well known is "Down the Rabbit-Hole", which is the first chapter from Alice's Adventures in Wonderland. The "§" symbol is commonly used to represent a chapter.

Mammoth by John Varley, has the chapters ordered in chronological order from the point of view of a non-time-traveler, but, as most of the characters travel through time, this leads to the chapters defying the conventional order

Many novels of great length have chapters. Non-fiction books, especially those used for reference, almost always have chapters for ease of navigation. In these works, chapters are often subdivided into sections. The chapters of reference works are almost always listed in a table of contents. Novels sometimes use a table of contents, but not always.

In ancient civilizations, books were often in the form of papyrus or parchmentscrolls, which contained about the same amount of text as a typical chapter in a modern book. This is the reason chapters in recent reproductions and translations of works of these periods are often presented as "Book 1", "Book 2" etc.

In the early printed era, long works were often published in multiple volumes, such as the Victorian triple decker novel, each divided into numerous chapters. Modern omnibus reprints will often retain the volume divisions. In some cases the chapters will be numbered consecutively all the way through, such that "Book 2" might begin with "Chapter 9", but in other cases the numbering might reset after each part (i.e., "Book 2, Chapter 1"). Even though the practice of dividing novels into separate volumes is rare in modern publishing, many authors still structure their works into "Books" or "Parts" and then subdivide them into chapters.